Decreasing Soil-Frost Depth and Its Relation to Climate Change in Tokachi, Hokkaido, Japan

Abstract

Frozen ground plays an important role in the energy and water cycle of cold regions, and affects the environment and agricultural practices in these regions. The effect of climate warming on soil frost is an important concern, but our present understanding of such effect is limited, due to the lack of long-term data covering a large region. This study analyzes a unique regional database of 20-year records from 1986-2005 of soil frost, combined with long-term climate data from 1955-2005. Annual maximum frost depths ðD max Þ in the Township of Memuro (514 km 2 ) in Tokachi, Hokkaido have decreased significantly in the last 20 years. The decrease in D max was caused by the development of thick snow cover in early winter that insulates the ground, not by the increase in air temperature. The D max is strongly correlated with a soil freezing index ðF 20 Þ, that integrates the combined effects of air temperature and snow cover. Using F 20 as a surrogate of D max , it was shown that the decreasing frost depth was a regional phenomenon occurring over the Tokachi Plain, covering an area of several thousand square kilometers. The timing of a major decrease in F 20 in the mid to late 1980's coincided with sharp decreases of snowfall in the Hokuriku region of Japan and the amount of drift ice in the southern part of the Sea of Okhotsk, both of which are regarded as indicators of the strength of the East Asian winter monsoon activities.

Soil-Frost Depth Change in Eastern Hokkaido under +2 K-World Climate Scenarios

“…Our interpretation can be applied to the case for a recent tendency in early-winter snowfall events and its subsequent decreace in soil-frost depth (Hirota et al 2006;Yazaki et al 2013a). The soil-frost depth was much sensitive to early-winter snowfall under the present climate, which was demonstrated in the difference between the two typical cases.…”

“…The coefficient C partly depends on the soil property, and we assume that C = 1.8, based on the observation at a site on volcanic-ash soil (Hirota et al 2006), mostly prevailed over eastern Hokkaido. The CFD is calculated from daily SAT and snow-depth (Fukuda 1982;Tsuchiya 1985) as where W is the period from 1 November to 28 February of the following year and the other notations are same as Eq.…”

“…For this local climate character, the soil frost was supposed to be much more affected by the snow depth. Hirota et al (2006) revealed a tendency of the decrease in soil-frost depth based on long-term observation at a site in Tokachi subprefecture (Fig. 1) …”

Effects of saturated hydraulic conductivity on volunteer potato (Solanum tuberosumL.) tuber survival

“…In the Tokachi region, a main crop production area in Japan, soil frost depth has decreased during the last 20 years because of the increase of the period during which soil is insulated from the cold air by thick snow cover (Hirota et al 2006). Boydston et al (2006) and Hirota et al (2011) reported that potato tubers (Solanum tuberosum L.) are killed when ambient soil temperatures drop below approximately -3°C.…”

Influences of snow cover and soil-frost on ground surface flux and soil gas concentration of CO2 in an agricultural land in northern Japan

“…In the northern hemisphere, snow-covered areas have been decreasing (IPCC, 2007). In the eastern part of Hokkaido, northern Japan, snowfall has been occurring earlier, and the soil frost depth has been decreasing in agricultural land year-by-year since late 1980 (Hirota et al, 2006). The marked decrease in frost depths results from the early development of snow cover, which insulates the ground.…”